The long-term objective of the proposed research is to understand recombination events that involve little or no DNA sequence homology. Such events have been detected in a number of ways. For example, when mammalian cells are transformed with DNA, the transforming sequences usually integrate into the chromosome by a non-homologous recombination event. In contrast, transforming DNA in the yeast Saccharomyces cerevisiae has been reported to integrate into the genome only by homologous recombination. Recently, integration of transforming DNA in yeast by non-homologous recombination has been observed. In this proposal, the rules governing this type of recombination will be examined. In particular, the genetic control of this type of exchange will be investigated by selecting mutants with higher (or lower) levels of illegitimate recombination. It will also be determined whether the illegitimate integration of transforming DNA is related to the formation of chromosomal deletions in yeast. Since illegitimate integration events are a serious problem in the development of protocols for gene therapy, these studies should be relevant to health-related problems. A second area of proposed research is the analysis of recombination events catalyzed by exogenously-added restriction enzymes. The use of this technique for insertional mutagenesis, and for the creation of chromosomal aberrations will be examined.